Fixed pixel site: problems when not fullscreened. I want to go relative

Hello,

I'm fairly new at coding, but have created a WordPress site for my band. It all comes out just how I want it to, assuming you have a screen resolution high enough for the site to fit in one window. I have overflow turned off for the whole site.

The problem I'm running into concerns the accessibility of those users who either don't open the site in a maximized window or have too small of a screen. Is there a way to re-size elements to fit into whatever window is opened? Maybe simply a way for it to look a bit better in smaller windows and enable overflow?